The book questions the humanity of humans increasingly urbanized and reliant on technology, implying that, for all their limits, the replicants might be more alive. Very influential on CyberPunk.
The movie Blade Runner touched on that theme, but it was undercut by Ridley Scott's position and direction that Rick Deckard was a replicant, as can be clearly seen in the director's cut. Then again, without seeing the director's cut, this is just another discussion amongst hardcore fans. There are other differences, as well: artificial animals, religious experiences mediated via machines, the importance of empathy (it shows in the film but in connection with the animals it is carried further).